Winteriziing runs the same initial price as turn-on/service calls. $85 for less than 12 zones, $95 for 13- 20, $125 for 20+. Commercial runs $200+.
We tag the main valve (almost always in the house), and remove and zip-tie the handle to the pipe.
Every customer who's blowout is after the Backflow is made aware that we cannot properly winterize anything before the POC, and we can cut one in at "X" price.
Leaking main valves are checked at the time of winterizing and we inform the customer of the problem, tell them the price, etc.
Any damage uncovered, or potential problems over the winter are documented on the invoice, which the customer signs.
Nothing is covered under freeze damage. Occasionally in the spring I may warentee something, but only if it's a really good customer, or someone who just spent a ton of money on a new system the previous year.
That's how we do.